Weaning presents many challenges to a young animal. These challenges include an abrupt change from a liquid to a solid diet that contains ingredients that may not be easily digestible to the young animal. Immediately after weaning, the digestive system of the animal has to adapt to a new feeding regime with respect to enzyme secretion. In addition, the young animal is presented with a new social structure. Combined, these effects disrupt nutrient intake that is necessary to maintain gut integrity and function. The reduced feed and water intake after weaning may contribute to intestinal inflammation, which may affect the structure of the villus and crypt. These disruptions in water and feed intake affect growth performance and are further exacerbated by an immature immune system. This creates susceptibility to digestive upsets and/or diarrhea.
In general, complex pelleted diets containing plasma protein and milk products have been used with some success to minimize postweaning lag in animals. However, it is not uncommon for a young animal to experience prolonged growth retardation.